The present invention relates to a display for preventing counterfeiting or copying of valuable stock certificates, such as gift tickets, or public documents, such as passports. The present invention further relates to a display which facilitates authenticity judgment with the naked eye and performs a function of preventing counterfeiting with high security, and to an information medium provided with the display.
A technique called watermarking is used for valuable stock certificates, such as paper currencies or gift tickets, or public documents, such as passports, for the purpose of preventing counterfeiting or imitation. Watermarking techniques have been known from long time ago as techniques for producing light and shade in an object. With this technique, when an object is observed by transmitting light therethrough, light and shade is produced with the change of intensity of the transmitted light so that one can confirm patterns, such as designs.
Methods of changing the intensity of transmitted light include, for example, a watermarking method in which the thickness of paper is slightly varied in fabricating the paper. These days as well, watermarking techniques are widely used as a means for preventing counterfeiting. However, the effects of preventing counterfeiting by these techniques are not sufficient because there is a risk that paper is patterned by means of oil or the like to create an imitation which can be perceived, at a glance, as a watermark. In such a situation, various techniques for preventing counterfeiting have been proposed, with which the effects can be confirmed by transmitting light through an object as is done with watermarks.
Further, as a display having visual effects that are different from those of a normal printed object, there is known a display that includes a diffraction grating which is formed by juxtaposing a plurality of grooves. For example, this display is able to display an image that changes in accord with observation conditions or is able to display a stereo mage. Iridescently shining spectral colors represented by the diffraction grating cannot be represented by a normal printing technique. For this reason, displays that include diffraction gratings are widely used for articles needing measures against counterfeiting.
PTL 1 proposes creating a pattern on a base, such as a colorless and transparent film with matte (rough) surface conditions, using a liquid material. The liquid material includes, for example, colorless and transparent acrylic lacquers that penetrate a rough surface and are dried. The patterned portions have light transmission properties greater than those in other portions to thereby provide a watermark pattern.
Further, in PTL 1, transparent thin films made of an inorganic compound are laminated to provide a multilayer interference film. When reflected light is observed from an interference film side, iridescently shining interference colors can be confirmed. Further, when transmitted light is observed from an opposite side of the interference film, complementary colors of specular reflection of the interference film side can be seen. Thus, a watermark pattern is permitted to coexist with flip-flop effects of the interference colors.
PTLs 2 and 4 propose a printed object obtained by printing a pattern with parallel lines on either one of the front and back of an object to be printed, and printing on the other side a pattern composed of streaks which are parallel lines applied with a design to be used as a latent image. When this printed object is seen by transmitting light therethrough, an image of a continuous tone can be confirmed, which appears as a result of merging of the patterns on the front and back.
PLTs 2 and 4 disclose a printed object in which a line pattern is printed on either of the front and back of an object through which light is transmitted. The other side of the printed object is printed with a pattern having a line array in synchrony with the line array of the line pattern on the one side and having approximately even streak widths perpendicular to the line array on the one side. The pitches of the line patterns on the front and back are changed by screen printing, while the front and back are aligned. Thus, the patterns on the front and back, as seen through transmitted light, are merged and the latent image appears as an image of a continuous tone.
PTL 3 proposes a printed object using watermarked paper having a concavo-convex configuration. The concavo-convex configuration is formed by a line pattern in which a design is represented by partially changing the angles of the lines, or a relief pattern, or by embossing the streak configuration of either of these patterns. In the watermarked paper, various line streaks with a predetermined interval therebetween are printed, with an inclination, onto portions other than the design portions having the concavo-convex configuration, using inks of colors excepting the color of the material and inks excepting transparent and colorless ink.
In the printed object of PTL 3, an irregular positional relationship is established between the concavo-convex configuration and the printed streaks having a predetermined interval therebetween. The irregular positional relationship exerts an effect of allowing one to recognize a specific letter, a motif, or the like as a latent image only when the printed object is seen from a specific angle. In addition, according to PTL 3, the watermarked paper exerts an effect of allowing one to easily recognize a watermark image through transmitted light.
PTL 5 describes that a plurality of diffraction gratings having grooves of different longitudinal directions or grating constants (i.e. pitch of grooves) are arranged to display a design. With the change of the position of an observer or a light source relative to the diffraction gratings, the wavelength of the diffracted light that reaches the observer's eye changes. Thus, using the above configuration, an iridescently changing image can be represented.
Image displays using diffraction gratings generally use relief-type diffraction gratings in which a plurality of grooves are formed. Usually, such a relief-type diffraction grating is obtained by manufacturing an original plate by photolithography and replicating the original plate.
However, lots of articles needing measures against counterfeiting come to use such an image display that includes a relief-type diffraction grating. As a result, this technique is now widely known. Along with this, there is a tendency that counterfeit articles are increasingly common. Therefore, it is now difficult to achieve sufficient effects of preventing counterfeiting using a display only characterized by iridescent light that is due to diffracted light.
PTL 6 discloses displaying a design with a combination of a diffraction grating pattern and a light scattering pattern. According to this, not only an iridescently changing image but also an image represented by light scattering can be displayed.
Further, PTL 7 describes a display that does not exert iridescent color change in accord with the change in position of a light or an observer, as is exerted by the relief-type diffraction grating pattern. Accordingly, visual effects different from those of the conventional diffraction grating are achieved.
PTLs 6 and 7 each describe a display that can exert visual effects greatly different from those of the iridescent color possessed by the conventional diffraction grating pattern. Accordingly, higher effects of preventing counterfeiting can be expected.